Firearms such as rifles generally have differing trigger pull weights depending on the application. The trigger pull weight is the amount of force required to cause a cocked firearm to discharge. Rifles for military issue generally have heavy pull weights to reduce the risk of unintentional discharge by inexperienced troops, or during rough handling during training or combat. Light trigger pull weights are generally preferred when long range accuracy is required, such as by military or police snipers, and by civilians engaged in target or sport shooting.
It is often desirable to make firearms more versatile, so that they are suited to more than one type of use. For instance, a government agency may wish to have only one or a limited number of standard rifles available, to facilitate simplified inventory, training and maintenance. Similarly, a civilian gun owner may prefer to have a single rifle that performs well for different applications instead of having to purchase a separate rifle for each application. In addition, collectors who prefer a particular type of rifle may wish to use it for different types of shooting or hunting activities.
A military rifle such as the Steyr AUG has a relatively heavy trigger pull weight of about 9 pounds. This is heavier than is generally preferred by civilian sport shooters and by those requiring precision long range shooting. Moreover, the AUG trigger requires the trigger to be pulled over this a relatively long distance, so that the total energy needed to pull the trigger is greater than if a 9-pound trigger with a short pull distance were employed. In addition, the bullpup design of the AUG positions the trigger well forward of the mechanism that releases the hammer, requiring long linkages that are prone to friction, further degrading trigger pull.
In the AUG rifle, a trigger spring provides the resistive force that determines the weight of pull. As in any firearms, a spring of different weight or strength may be substituted to achieve a desired weight or pull. However, this requires a user to determine in advance what the desired weight might be, or to try several samples or springs until a desired weight is achieved. Moreover, unless several different springs are owned, the user is limited to only as many weight options as springs he owns. This presents challenges for a soldier in the field seeking to modify the trigger weight, when parts supplies are unavailable. Alternative weight springs must be stored, and may be lost. In addition, a supplier must manufacture and stock a range of different springs to provide a range of different weights, increasing inventory and manufacturing cost.